Many products are packed under a protective atmosphere, which method is commonly known as modified atmosphere packaging (MAP). It is in particular applied for food products such as meat, fish, fruit, vegetables, instant meals, pastry, or potato crisps. Other products that may be MAP-packed are cosmetics, medicaments, chemicals and sterile objects such as medical or laboratory instruments (e.g. needles, syringes, bandages). Often, the applied modified atmospheres have a reduced oxygen content and an increased nitrogen and/or carbon dioxide content. However, in certain cases, an atmosphere rich in oxygen is used.
On the way to the consumer, the protective atmosphere of a MAP-package can be impaired at many stages. The package can for example be damaged by inappropriate handling during production, transport or placement in a store or working space, thereby creating an open connection with the outside environment. Also, mistakes can be made during the process of packaging, for example the package may be inadequately sealed or the gas that is used for creating the protective atmosphere is of the wrong composition. As a result, large amounts of (food) products become unsuitable for use or consumption and need to be disposed, for example by the manufacturer/packager, carrier, store, hospital, laboratory or end-user. In addition, there is a waste of packaging material.
By measuring the composition of the atmosphere in a MAP-package, it is possible to identify MAP-packages that are not suitable for use by the end-user. Preferably, this is performed at an early stage, for example already at the production/packaging line. Conventional measuring methods are often invasive, i.e. the atmosphere is permanently impaired after the measurement and the product is not suitable anymore for the intended use. In addition, such measurements are usually made on a random sample representing an entire batch. As a result, an entire batch can be rejected on the basis of one sample. Conversely, it is possible that improperly packed articles inadvertently pass a quality control and find their destiny at the end-user. A so-called “100% check” with a non-invasive method would therefore be desired. This would not only be useful at the production/packaging line, but also for the end-user. It can offer the certainty that the product he/she is intended to buy or use is indeed still in a protective atmosphere. However, it is usually too complicated and too expensive to test each and every package, because this requires that means for sensing oxygen are included in every MAP-package.
Providing every MAP-package with sensing means is conventionally done for example by using an unlaminated patch that can measure the inner atmosphere, which patch is glued to the inside of the foil. Placing and gluing such patches is costly, time-consuming and difficult to integrate in current processes for making foils and MAP-packages. Moreover, there is a risk that patches come loose from the foil and get in direct contact with the product. Thus far, unlaminated patches seem only to be used for research purposes and product development.
A packaging foil with an attached oxygen sensor is known from, for example, WO2007120637 A2. This publication describes a food packaging membrane for a sealable package, comprising a luminescence indicator capable of detecting one or more analytes within the package contacting the membrane. The detection is performed with a sensor comprising a ruthenium-based luminescence compound dispersed within a diffusible polymer matrix. A disadvantage of such membrane is that the sensor needs to be in fluid communication with the package interior and the contents of the package, i.e. that a gas flow is required between the main headspace of the packaging and the sensor material. In this way, the sensor may come into direct physical contact with the contents of the packaging and thereby contaminate such contents. This is undesired, in particular when the contents are edible products. Another disadvantage is that the matrix with the luminescence compound has to meet the requirements of high structural integrity (i.e. it is not subject to distortion or abrasion by physical contact with the contents of the package) and strong adhesion (i.e. it is not wiped away from the surface by physical contact with the contents of the package.
It is therefore an objective of the invention to provide a packaging foil with oxygen sensing means that can be used to prepare a MAP-packaging wherein the presence of oxygen in the atmosphere of the packaging can be determined in a non-invasive manner. In particular, it is aimed that it can be determined whether the amount of oxygen lies above a certain level, or that the presence of oxygen is determined in a quantitative way.
It is also an objective to provide a packaging foil with oxygen sensing means that can be introduced in a conventional process for packaging articles wherein each produced packaging contains the oxygen sensing means.
It is also an objective of the invention to provide a packaging comprising an object enclosed by the packaging and comprising oxygen sensing means that can measure the oxygen in the atmosphere surrounding the object, wherein the oxygen sensing means cannot come into physical contact with the object present in the packaging.
It has now been found that one or more of these objectives can be reached by using a particular combination of foils and a luminescent dye in a particular arrangement.
Accordingly, the present invention relates to a multi-layered packaging foil comprising                a layer L-1 having an oxygen gas transmission rate OGTR-1;        a luminescent compound having the property that its luminescence is capable of being quenched by oxygen;        a layer L-2 adhering to L-1 and to the luminescent compound, the layer L-2 having an oxygen gas transmission rate OGTR-2 that is at least 20 times higher than OGTR-1;wherein the luminescent compound is present between L-1 and L-2.        